1. Field of Invention
The present invention relates to a seat suspension provided with a body-weight adjusting device and, in particular, relates to a seat suspension of this type having a thin, or shallow, structure especially suitable for seats installed in vehicles of smaller size.
2. Description of the Prior Art
While a seat suspension possessing a body-weight adjusting device has been employed in vehicles generally of the larger size category, proposals have been made to provide such a seat suspension in smaller size vehicles as well. However, due to limitations of space typical of smaller vehicles, the seat is necessarily somewhat taller when such a body-weight adjustable seat suspension is provided therein. This, of course, poses a problem for the use of a seat suspension having such a capability in smaller sized vehicles.
By way of example, a typical seat suspension of the aforesaid type will be briefly described with reference to FIG. 1 and 2 of the accompanying drawings. In FIG. 1, (1) and (2) designate an upper frame and a lower frame, respectively, of a seat. Lower frame (2) is formed substantially in a rectangular shape and made of a metallic frame substantially channel-shaped in section with the opening defined in the thus channel-shaped frame being faced to each other inwardly to the frame. Upper frame (1) is basically formed in a flat, plate-like shape with both the lateral portions thereon, or the operationally required portions thereof, being bent downwards. The frame is made of metallic material of a configuration substantially conforming to that of lower frame (2). To this upper frame (1), a cushion member is mounted, using what may be termed a "cushion pan" (not shown).
Between upper frame (1) and lower frame (2), there is interposed a pair of X-shaped links (3) which constitute a seat suspension. This seat suspension is of a well-known type and comprises two links (4) and (5) rotatably, pivotally supported at pivot means (6) substantially centrally of each link. Upper end portion (5b) of each of links (4) and (5) is rotatably fixed by pivot means (7) to upper frame (1) rearwardly to the links, whereas lower end portion (4b) thereof is rotatably fixed by pivot means (8) to lower frame (2) with the other lower end portion portion (5b) being slidably secured to lower frame (2) by means of a roller (9), or the like, so as to be movable forwardly and rearwardly relative to lower frame (2). The forwardly-located upper end portions (4a) of X-shaped links (3) are coupled by means of a frame member (10) extended therebetween, thereby supporting the forward portion of upper frame (1) in a direction from the bottom of the seat. The rearwardly-located upper end portions (5a) are coupled by means of a frame member (11) to which a pair of tension springs (12) are secured one at each end thereof.
With reference to both FIG. 1 and 2, a bell crank (14) is rotatably fixed by pivot means (13) to the inner surface of upper frame (1) in such an arrangement that one end portion thereof is engaged with a nut (21) of an adjusting spindle (15) while the other end portion thereof is rotatably connected to one end of a tension frame (16) by means of pivot means (17). Tension frame (16) is connected at the other end thereof to the center portion of an equalizer frame (18) by pivot means (19) so as to be rotatable about said pivot means. Equalizer frame (18) is secured at both ends thereof to the other ends of the foregoing pair of tension springs (12), respectively. Adjusting spindle (15) consists of a rotary shaft with a thread (20) partially formed thereon, nut (21) being engaged with said thread.
Substantially at the center of the thus-constructed seat, a shock absorber (22) is arranged such that the one end thereof is rotatably affixed to the rear frame section of lower frame (2) and the other end is rotatably fixed to rod (10).
In the above-described conventional seat suspension arrangement, when coupled by a person, the seat moves downwardly due to the occupant's weight pressing upon and lowering X-shaped links (3) provided thereunder thereby reducing the height of upper frame (1). However, in this instance, although the seat suspension is compressed into a relatively thin shape, yet by reason of the fact that shock absorber (22) extends centrally between the pair of X-shaped links (3) obliquely thereto and tension springs (12) are disposed above the X-shaped links centrally thereof, the total height of the seat suspension involves protruding elements at its center portion and consequently the seat suspension is prevented from assuming a lower, or more shallow, profile.